Garbage collection system in MuranoPL¶

Garbage collector methods¶

Murano garbage collector class (io.murano.system.GC) has the following methods:

collect()

Initiates garbage collection of unreferenced objects of current deployment. Usually, it is called by murano ObjectStore object during deployment. However, it can be called from MuranoPL code like io.murano.system.GC.collect().

isDestroyed(object)

Checks if the object was already destroyed during a GC session and thus its methods cannot be called.

isDoomed(object)

Can be used within the .destroy() method to check if another object is also going to be destroyed.

subscribeDestruction(publisher, subscriber, handler=null)

Establishes a destruction dependency from the subscriber to the object passed as publisher. This method may be called several times with the same arguments. In this case, only a single destruction dependency will be established. However, the same amount of calls of unsubscribeDestruction will be required to remove it.

The handler argument is optional. If passed, it should be the name of an instance method defined by the caller class to handle the notification of publisher destruction. The following argument will be passed to the handler method:

object

A target object that is going to be destroyed. It is not recommended persisting the reference to this object anywhere. This will not prevent the object from being garbage collected but the object will be moved to the “destroyed” state. This is an advanced feature that should not be used unless it is absolutely necessary.

unsubscribeDestruction(publisher, subscriber, handler=null)

Removes the destruction dependency from the subscriber to the object passed as publisher. The method may be called several times with the same arguments without any side effects. If subscribeDestruction was called more than once, the same (or more) amount of calls to unsubscribeDestruction is needed to remove the dependency.

The handler argument is optional and must correspond to the handler passed during subscription if it was provided.

Using destruction dependencies¶

To use direct destruction dependencies in your murano applications, use the methods from MuranoPL io.murano.system.GC. To establish a destruction dependency, call the io.murano.system.GC.subscribeDestruction method in you application code:

.init:
   Body:
     - If: $.publisher
       Then:
         - sys:GC.subscribeDestruction($.publisher, $this, onPublisherDestruction)

In the example above, onPublisherDestruction is a Foo object method that will be called when Bar is destroyed. If you do not want to do something specific with the destroyed object omit the third parameter. The destruction dependencies will be persisted between deployments and deserialized from the objects model to murano object.